1. Field of the Invention
The present invention relates to a digital broadcasting, and more particularly, to a method for identifying extender text tables of an electronic program guide in a digital television.
2. Description of the Related Art
Generally, video and audio streams are compressed as digital information while system and program information are compressed in accordance with a program and system information protocol (PSIP) to provide digital broadcasting. Here, program information is decoded from data other than the video and audio information, and displayed on a screen for a user through an electronic program guide (EPG). The EPG and system information are combined into the PSIP and as the ATSC standard for ground wave and cable digital broadcasting, the PSIP provides a variety of information on programs by parsing messages encoded through a moving picture experts group (MPEG-2, ISO/IEC 13818-1 system) method (1997 DEC. document A/65).
The PSIP includes a plurality of tables to transmit and receive A/V data generated in MPEG-2 video and AC-3 audio formats, and to transmit information and programs on channels of broadcasting stations. Accordingly, the PSIP enables a primary function of providing A/V services for broadcast programs of selected channels as well as a secondary function of providing guide services, i.e. EPG, for the broadcast programs. Particularly, information such as information on channels for channel-selecting and packet identification digits (PID) for A/V reception is transmitted through a virtual channel table (VCT), while EPG information on broadcast programs for the channels is transmitted through an event information table (EIT).
The EIT is information regarding the events of virtual channels and includes a title and start time of each event. Here, an event is typically a TV program. Also, the PSIP can transmit at least four and at most one hundred twenty eight EITs in the format of EIT-k, where each EIT provides an event information of a specific time band.
The PSIP further includes a system time table (STT) which provides time information; a rating region table (RRT) which transmits information on regions and rating organizations, i.e. ranking programs; an extender text table (ETT) which further explains channels and broadcast programs; and a master guide table (MGT) which manages the version and PID of each table. These tables are transmitted by data structures called sections. Namely, a section is the elementary unit of each table and one or more section(s) are combined to form a complete table. Accordingly, to facilitate user interface, the EPG representing information on programs to be broadcasted on a digital television (DTV) has a variety of formats depending on the section(s) defining a table.
A widely used format of the EPG is by using a Gemstar table. In such format, an ETT which contains detailed information on an event, i.e. a broadcast program, can have event information corresponding to a unit of three hours. Also, each event information is represented and identified by an index based on a chronological order of EIT-1, EIT-1, EIT-127. Thus, an ETT is mapped with each corresponding EIT, i.e. event information corresponding to EIT-0 is mapped with ETT-0, event information corresponding to EIT-1 is mapped with ETT-1, . . . , and event information corresponding to EIT-127 is mapped with ETT-127. Here, an EIT can also represent information on events of up to three hours in a single section, where each event has an event_id field for identifying the event and an ETM_location field for displaying whether an ETT which contains detailed information on the event is present.
Furthermore, each section of the ETT comprises an ETM_id representing an event or a channel as well as detailed text information on the event or channel. The sections of tables used in PSIP have syntax types as follows.
table_id8 bitssection_syntax indicator1 bitsprivate_indicator1 bitsreserved2 bitssection_length12 bits table_id_extension16 bits reserved2 bitsversion_number5 bitscurrent_next_indicator1 bitssection_number8 bitslast_section_number8 bitsprotocol_number8 bitsactual_table_data*CRC_3232 bits 
The table sections, as listed above, can be for section headers of tables which have common rules of composition or for section bodies of tables which have different contents depending on the objective of a table. Here, a section header has basic information such as table_id, table_id_extension, version_number, and section_number, which identifies a section in the section header. Specific field value(s) based on such basic information which identify section(s) within the section header can be used to extract certain section(s). Namely, the section(s) with basic information which match the specific field value(s) can be extracted. This process is known as section filtering.
General formats of EIT and ETT are shown in FIG. 1. As shown, a section EIT-0 within an EIT includes a plurality of events, where each event is distinguished or identified by the event_id and the ETM_location indicates whether an ETT exists for the identified event. Also, an ETM_id within each ETT section is represented by a source_id+event_id+1 sb and indicates the event to which the ETT section corresponds. For example, in the ETM_id of ‘XX . . . X00000000000011XX’ shown in FIG. 1, the underlined portion represents an event mapped with a corresponding event_id. In other words, an ETT-0 has a link with a corresponding event through the ETM_id in the section body.
However, information in the section header of the ETT-0 such as the table_id, the table_id_extension, the section_number, and the last_section_number includes the same value of ‘00000000000011’ regardless of the section. Namely, each section has the same section header, excluding the version field. Thus, to process an ETT, required contents of the ETT are randomly extracted through a section header filtering according to a sequential process as shown in FIG. 2.
Referring to FIG. 2, an ETT section filter is first set (S1) and the ETT section-outs, which have been received, are detected (S2). All received ETT sections are then input (S3) and the input ETT sections are parsed (S4). Next, an ETM_id is detected depending on the result obtained from parsing the ETT sections (S5) and the detected ETM_id is compared with an event_id to determine if the values are identical (S6). If the detected ETM_id is identical to the event_id, the ETM_id is stored as a text message (S8) and the processing of the ETT ends. Otherwise, the corresponding section is dumped (S7) and a next ETM_id is detected and compared to the event_id by repeating the above process.
However, a method for identifying ETTs of an EPG of a DTV according to the related art has the following problems.
First, because the section headers of ETT sections are basically identical, a general section filtering cannot be conducted. Thus, all sections of, for example, ETT-0 corresponding to an EIT-0 are received and parsed to select a required ETT-0 section, resulting in a repeated processing of an ETT section. Second, upon receiving a command to identify whether the contents of an ETT-0 section has been changed when a version number is altered, the entire ETT-0 sections must be parsed to detect an ETM_id. Third, if ETT sections are not the same version, a section filtering based on the version cannot be performed. In other words, the method, in which different sections of the ETT-0 have the same section header, fails to meet the system standard of the moving picture experts group (MPEG) as well as to perform a section filtering of sections using the header.